The present invention relates to ferrite magnetic powder and a magnet using the magnetic powder, and to method for producing them.
Ferrite is a generic name of a compound composed of an oxide of divalent cation metal and a trivalent iron. A ferrite magnet is used for various applications including motors, generators, and the like. As a raw material of a ferrite magnet, Sr ferrite (SrFe,12O19) or Ba ferrite (BaFe,12O19) having a hexagonal structure of magnetoplumbite type is widely used. These kinds of ferrite are relatively inexpensively produced by using an iron oxide and a carbonate of strontium (Sr), barium (Ba), or the like as raw materials by means of powder metallurgy.
The fundamental composition of the magnetoplumbite-type ferrite is generally represented by a chemical formula of MO.6Fe2O3. An element M is a metal of divalent cation, and is selected from a group consisting of Sr, Ba, Pb, and the like.
It has been reported that, in Ba ferrite, when Ti and Zn were substituted for part of Fe, the magnetization was improved (see Journal of the Magnetics Society of Japan vol. 21, NoS2(1997)69-72).
In addition, it has been known that, in Ba ferrite, when La was substituted for part of Ba, and Co and Zn were substituted for part of Fe, the coercive force and the magnetization were improved (see Journal of Magnetism and Magnetic Materials vol. 31-34, (1983)793-794, Bull. Acad. Sci. USSR (Transl.), phys. Sec. vol.25 (1961) 1405-1408).
In Sr ferrite, it has been reported that, when La was substituted for part of Sr, and Co and Zn were substituted for part of Fe in the same manner as described above, the coercive force and the magnetization were improved (see International Application No.PCTJP98/00764, and International Publication No.WO98/38654).
In these ferrite magnets, however, the property improvement in both of the coercive force and the saturation magnetization is also sufficient. As for a composition in which Ti and Zn are substituted for Fe, the saturation magnetization is increased, but the coercive force is decreased.
Moreover, raw materials such as La, Co, and the like are expensive, and there arises a problem in that, if a large amount of such raw materials is used, the raw material cost is increased.
The invention has been conducted in view of the above-mentioned problems. It is a main object of the invention to provide ferrite magnetic powder and a magnet using such magnetic powder in which both of the saturation magnetization and the coercive force ate further improved at a low cost.
The magnetic powder according to the present invention is magnetic powder including ferrite having a hexagonal structure expressed by (1xe2x88x92x)SrO.(x/2)La2O3.(nxe2x88x92y/2xe2x88x92yxe2x80x2/2xe2x88x92yxe2x80x3/2)Fe2O3.yTiO2.yxe2x80x2ZnO.yxe2x80x3CoO as a primary phase, wherein x, y, yxe2x80x2 and yxe2x80x3 designating mole ratios meet 0.1xe2x89xa6xxe2x89xa60.3, 0.01xe2x89xa6yxe2x89xa60.3, 0xe2x89xa6yxe2x80x2xe2x89xa60.3, 0.1xe2x89xa6yxe2x80x3xe2x89xa60.4, and 5.5 xe2x89xa6nxe2x89xa66.5.
The bonded magnet of the present invention is characterized by including the above-mentioned magnetic powder.
The sintered magnet of the present invention is characterized by being formed from the above-mentioned magnetic powder. The sintered magnet includes CaO, SiO2, Cr2O3, and Al2O3, and the adding amounts thereof preferably satisfy the following conditions of CaO : not lower than 0.3 wt % nor higher than 1.5 wt %, SiO2: not lower than 0.2 wt % nor higher than 1.0 wt %, Cr203: not lower than 0 wt % nor higher 5.0 wt %, and Al2O3: not lower than 0 wt % nor higher than 5.0 wt %.
The method for producing a ferrite calcined body of the present invention includes the steps of: preparing mixed raw material powder in which respective oxide powder of La, Ti, Zn, and Co are added to raw material powder of SrCO3 and Fe2O3; and calcining the mixed raw material powder, thereby forming a calcined body of ferrite having a composition of (1xe2x88x92x)SrO.(x/2)La2O3.(nxe2x88x92y/2xe2x88x92yxe2x80x2/2xe2x88x92yxe2x80x3/2)Fe2O3.yTiO2yxe2x80x2ZnO.yxe2x80x3CoO(0.1xe2x89xa6xxe2x89xa60.3, 0.01xe2x89xa6yxe2x89xa60.3, 0xe2x89xa6yxe2x80x2xe2x89xa60.3, 0.1xe2x89xa6yxe2x80x3xe2x89xa60.4, and 5.5xe2x89xa6nxe2x89xa66.5).
The method for producing magnetic powder according to the present invention includes the steps of: preparing mixed calcined body powder in which CaO, SiO2, Cr2O3, and Al203(CaO: not lower than 0.3 wt % nor higher than 1.5 wt %, SiO2: not lower than 0.2 wt % nor higher than 1.0 wt %, Cr2O3: not lower than 0 wt % nor higher than 5.0 wt %, and Al203: not lower than 0 wt % nor higher than 5.0 wt %) are added to a calcined body produced by the above-mentioned method for producing a ferrite calcined body; and pulverizing the mixed calcined body powder.
Another method for producing magnetic powder according to the present invention includes the steps of: preparing mixed raw material powder in which respective oxide powder of La, Ti, Zn, and. Co are added to raw material powder of SrCO3 and Fe2O3: calcining the mixed raw material powder, thereby forming a calcined body of ferrite having a composition of (1xe2x88x92x)SrO.(x/2)La2O3.(nxe2x88x92y/2xe2x88x92yxe2x80x2/2xe2x88x92yxe2x80x3/2)Fe2O3.yTiO2.yxe2x80x2ZnO.yxe2x80x3CoO(0.1xe2x89xa6xxe2x89xa60.3, 0.01xe2x89xa6yxe2x89xa60.3, 0xe2x89xa6yxe2x80x2xe2x89xa60.3, 0.1xe2x89xa6yxe2x80x3xe2x89xa60.4, and 5.5xe2x89xa6nxe2x89xa66.5); and pulverizing the calcined body.
The step of preparing mixed raw material powder includes, in addition to a case where the mixed raw material powder is prepared from the beginning, a case where mixed raw material powder which is prepared by another person is purchased and employed, and a case where powder prepared by another person is mixed.
Preferably, the calcination is performed at temperatures of not lower than 1100xc2x0 C. nor higher than 1450xc2x0 C.
More preferably, the calcination is performed at temperatures of not lower than 1300xc2x0 C. nor higher than 1400xc2x0 C.
The method for manufacturing a magnet according to the present invention includes the steps of: preparing mixed raw material powder in which respective oxide powder of La, Ti, Zn, and Co are added to raw material powder of SrCO3 and Fe2O3; calcining the mixed raw material powder, thereby forming a calcined body of ferrite having a composition of (1xe2x88x92x)SrO.(x/2)La2O3.(nxe2x88x92y/2xe2x88x92yxe2x80x2/2xe2x88x92yxe2x80x3/2)Fe2O3.yTiO2yxe2x80x2ZnO.yxe2x80x3CoO(0.1xe2x89xa6xxe2x89xa60.3, 0.01xe2x89xa6yxe2x89xa60.3, 0xe2x89xa6yxe2x80x2xe2x89xa60.3, 0.1xe2x89xa6yxe2x80x3xe2x89xa60.4, and 5.5xe2x89xa6nxe2x89xa66.5); preparing a mixed calcined body by mixing additives such as CaO, SiO2, Cr2O3, and Al2O3 with the calcined body, pulverizing the mixed calcined body, and forming ferrite magnetic powder; and molding and sintering the ferrite magnetic powder.
The method for manufacturing a bonded magnet according to the invention includes the steps of: preparing mixed raw material powder in which respective oxide powder of La, Ti, Zn, and Co are added to raw material powder of SrCO3 and Fe2O3; calcining the mixed raw material powder, thereby forming a calcined body of ferrite having a composition of (1xe2x88x92x)SrO.(x/2)La2O3.(nxe2x88x92y/2xe2x88x92yxe2x80x2/2xe2x88x92yxe2x80x3/2)Fe2O3.yTiO2yxe2x80x2ZnO.yxe2x80x3CoO(0.1xe2x89xa6xxe2x89xa60.3, 0.01xe2x89xa6yxe2x89xa60.3, 0xe2x89xa6yxe2x80x2xe2x89xa60.3, 0.1xe2x89xa6yxe2x80x3xe2x89xa60.4, and 5.5xe2x89xa6nxe2x89xa66.5); pulverizing the calcined body and forming ferrite magnetic powder; annealing the ferrite magnetic powder; and forming a bonded magnet from the annealed ferrite magnetic powder.
Preferably, the calcination is performed at temperatures of not lower than 1100xc2x0 C. nor higher than 1450xc2x0 C.
More preferably, the calcination is performed at temperatures of not lower than 1300xc2x0 C. nor higher than 1400xc2x0 C.
Preferably, the annealing is performed at temperatures of not lower than 700xc2x0 C. nor higher than 1100xc2x0 C.
Another magnetic powder according to the present invention is magnetic powder including ferrite having a hexagonal structure expressed by
(1xe2x88x92x)AO.(x/2)R2O3.(nxe2x88x92y/2xe2x88x92yxe2x80x2/2)Fe2O3.yTiO2yxe2x80x2MeO as a primary phase, wherein the element A is at least one kind of element selected from a group consisting of Sr, Ba, Ca, and Pb, the element R is at least one kind of element selected from a group consisting of rare earth elements including Y and Bi, the element Me includes at least one kind of element selected from a group consisting of Co, Ni, and Zn, and
x, y, and yxe2x80x2 designating mole ratios meet 0.1xe2x89xa6xxe2x89xa60.3, 0.01xe2x89xa6yxe2x89xa60.3, 0.1xe2x89xa6yxe2x80x2xe2x89xa60.4, and 5.5xe2x89xa6nxe2x89xa66.5.
Preferably, the magnetic powder is calcined at temperatures of not lower than 1100xc2x0 C. nor higher than 1450xc2x0 C.
More preferably, the magnetic powder is calcined at temperatures of not lower than 1300xc2x0 C. nor higher than 1400xc2x0 C.
The magnet of the present invention is characterized by being formed from the above-mentioned magnetic powder.